Install modified MultiROM manager, currently in MultiROM manager from Play store ubuntu image server is hardcoded to system-image.tasemnice.eu. However thanks to user @sedrubal on Github, MultiROM Manager is patched to use kubuntu.plasma-mobile.org instead of system-image.tasemnice.eu server.

This is final step to get Plasma Mobile installed. Open the MultiROM manager installed from the previous step. In the Install Ubuntu Touch card, select the devel or devel-proposed channel and hit install. It will download the files on your device, this takes time according to your internet connection speed. Once done it will ask you to reboot system. Hit OK.

It will reboot to recovery and perform the installation of Plasma Mobile. This process takes 15 to 20 minutes.

Once done at boot you will be asked to choose between Internal rom and newly installed Plasma Mobile image.